Reversible Phase Transformation and Mechanochromic Luminescence of Zn II ‐Dipyridylamide‐Based Coordination Frameworks

A 1D double‐zigzag framework, {[Zn(paps) 2 (H 2 O) 2 ](ClO 4 ) 2 } n ( 1 ; paps= N , N ′‐bis(pyridylcarbonyl)‐4,4′‐diaminodiphenyl thioether), was synthesized by the reaction of Zn(ClO 4 ) 2 with paps. However, a similar reaction, except that dry solvents were used, led to the formation of a novel 2D polyrotaxane framework, [Zn(paps) 2 (ClO 4 ) 2 ] n ( 2 ). This difference relies on the fact that water coordinates to the Zn II ion in 1 , but ClO 4 − ion coordination is found in 2 . Notably, the structures can be interconverted by heating and grinding in the presence of moisture, and such a structural transformation can also be proven experimentally by powder and single‐crystal X‐ray diffraction studies. The related N , N ′‐bis‐ (pyridylcarbonyl)‐4,4′‐diaminodiphenyl ether (papo) and N , N ′‐(methylenedi‐ para ‐phenylene)bispyridine‐4‐carboxamide (papc) ligands were reacted with Zn II ions as well. When a similar reaction was performed with dry solvents, except that papo was used instead of paps, the product mixture contained mononuclear [Zn(papo)(CH 3 OH) 4 ](ClO 4 ) 2 ( 5 ) and the polyrotaxane [Zn(papo) 2 (ClO 4 ) 2 ] n ( 4 ). From the powder XRD data, grinding this mixture in the presence of moisture resulted in total conversion to the pure double‐zigzag {[Zn(papo) 2 (H 2 O) 2 ](ClO 4 ) 2 } n ( 3 ) immediately. Upon heating 3 , the polyrotaxane framework of 4 was recovered. The double‐zigzag {[Zn(papc) 2 (H 2 O) 2 ](ClO 4 ) 2 } n ( 6 ) and polyrotaxane [Zn(papc) 2 (ClO 4 ) 2 ] n ( 7 ) were synthesized in a similar reaction. Although upon heating the double‐zigzag 6 undergoes structural transformation to give the polyrotaxane 7 , grinding solid 7 in the presence of moisture does not lead to the formation of 6 . Significantly, the bright emissions for double‐zigzag frameworks of 1 and 3 and weak ones for polyrotaxane frameworks of 2 and 4 also show interesting mechanochromic luminescence.